Preparing formulations of therapeutic agents that have low solubility in water and delivering the agents to a target tissue have been a major challenge for pharmacologists and therapeutic agent delivery scientists. See Gaudana R. et al., Ocular Therapeutic agent Delivery, AAPS J., 12(3): 348-360 (2010). The combined effect of the unique anatomy and physiology of the eye and the low water solubility of the therapeutic agents for treating ocular diseases or disorders have frustrated the delivery of these agents to a desired target site of the eye. See Gaudana. There is, therefore, a need for formulations and delivery systems, which will allow high solubility of the therapeutic agents and improve stability and efficacy at the target tissues.
Protein kinases have been implicated in ocular diseases, not limited to, but including age related macular degeneration (hereinafter “AMD”), diabetic macular edema and proliferative diabetic retinopathy. Transmembrane receptor protein kinases exhibit an extracellular domain, capable of ligand binding. These ligand binding mechanisms trigger activation of the kinase catalytic domain which initiates a cascade of signals that controls intracellular functions.
Examples of receptor protein kinase are growth factors such as EGF, FGF, VEGF, PDGF and IGF. Elevated levels of soluble growth factors, such as vascular endothelial growth factor-A (VEGF), have been found in ocular tissues and fluids removed from patients with pathologic ocular angiogenesis. Various ocular tissues including the neurosensory retina and retinal pigmented epithelium (RPE) are known to respond to hypoxia, inflammation, and trauma by increasing VEGF expression that can lead to blood-retina barrier breakdown (i.e., enhanced vascular permeability and extracellular edema) and/or pathologic neovascularization (NV).
Delivery of therapeutic agents in the eye is challenging. Major drawbacks exist in the current delivery means because of the recurrent intravitreal injections required for chronic maintenance therapy. Repeated intravitreal injections present both a risk and a burden to patients. Endophthalmitis, retinal detachments, traumatic cataract, and increased intraocular pressure (IOP) are all potential vision-threatening sequela to the intravitreal route of administration. Moreover, monthly treatment or even monthly monitoring is a substantial burden to patients, their caregivers, and to the medical community, especially when considering that treatment may need to persist for a patient's lifetime. While roughly one-third of patients experience improved vision when treated with repeated intravitreal injections of certain biologic VEGF inhibitors, the majority of patients experience only stabilization of reduced vision.
Formulations may provide less than ideal stability in one or more ways when injected into a therapeutic device in at least some instances. For example, a buffer of the injected formulation may be released from the device into the vitreous in at least some instances. Also, diffusion of hydrogen ions and hydroxide ions between the reservoir and the vitreous may affect the pH of the formulation within the device.
In at least some instances, a buffer of a fluid of the eye such as the vitreous humor having a physiological pH may enter the device and affect the pH of the formulation within the device, such that the stability of the therapeutic agent may be less than ideal in at least some instances.
In at least some instances, formulation components added to increase the solubility of the therapeutic agents may bind the therapeutic agent so strongly that efficacy at the target tissue may be less than ideal in at least some instances.
In light of the above, it is desirable to provide improved formulations of therapeutic agents for therapeutic devices that overcome at least some of the above deficiencies of the known formulations, for example with improved therapeutic agent release that can be maintained over an extended time when implanted.
Systems described here comprise a therapeutic device for intravitreal delivery of a therapeutic agent, and a formulation comprising the therapeutic agent. The systems disclosed here extends the half-life of a therapeutic agent in the vitreous humor of the eye.